Kinetic Analysis about the Effects of Neutral Salts on the Thermal Stability of Yeast Alcohol Dehydrogenase

The effects of salts on the rate constants of inactivation by heat of yeast alcohol dehydrogenase (YADH) at 60.0°C were measured. Different effects were observed at low and high salt concentrations. At high concentrations, some salts had stabilizing effects, while others were destabilizing. The effects of salts in the high concentration range examined can be described as follows: (decreased thermal stability) NaClO₄ < NaI = (C₂H₅)₄NBr < NH₄Br < NaBr = KBr = CsBr = (no addition) < (CH₃)₄NBr < KCl < KF < Na₂SO₄ (increased thermal stability). The decreasing effect of NaClO₄ on YADH controlled the thermal stability of the enzyme absolutely and was not compensated by the addition of Na₂SO₄, a salt which stabilized the enzyme. However, Na₂SO₄ compensation did occur in response to the decrease in thermal stability caused by (C₂H₅)₄NBr. The rate constants of inactivation by heat (k [subscript in]) of the enzyme were measured at various temperatures. Effective values of the thermodynamic activation parameters of thermal inactivation, activation of free energy ([Delta]G